Sums of Reciprocal Eigenvalues of the Laplacian

The purpose of this paper is to present formulas for the sum of the squares of all reciprocal eigenvalues λ ofthe fixed membrane and the free membrane μ for plane simply connected domains. As a consequence we obtain that among all simply connected plane domains with the maximal conformal radius 1 and the area A only the unit disk yields the minimum of .     

Sharp bounds for the first non-zero Stekloff eigenvalues

Let (M,,) be an n(2)-dimensional compact Riemannian manifold with boundary and non-negative Ricci curvature. Consider the following two Stekloff eigenvalue problems

where Δ is the Laplacian operator on M and ν denotes the outward unit normal on ∂M. The first non-zero eigenvalues of the above problems will be denoted by p₁ and q₁, respectively. In the present paper, we prove that if the principle curvatures of the second fundamental form of ∂M are bounded below by a positive constant c, then with equality holding if and only if Ω is isometric to an n-dimensional Euclidean ball of radius , here λ₁ denotes the first non-zero eigenvalue of the Laplacian of ∂M. We also show that if the mean curvature of ∂M is bounded below by a positive constant c then q₁nc with equality holding if and only if M is isometric to an n-dimensional Euclidean ball of radius . Finally, we show that q₁A/V and that if the equality holds and if there is a point x₀∂M such that the mean curvature of ∂M at x₀ is no less than A/{nV}, then M is isometric to an n-dimensional Euclidean ball, being A and V the area of ∂M and the volume of M, respectively.     

The inclusion of Stekloff eigenvalues by boundary data approximation

We give eigenvalue inclusion theorems allowing the computation of both-sided Stekloff-eigenvalue bounds from a given approximate eigenpair. We demonstrate in numerical examples the possibility to get close bounds for even higher eigenvalues using the boundary collocation method. A good choice for trial functions are singularity functions allowing a control for the numerical stability and—in theory—an eigenvalue inclusion in an arbitrary small interval.The inclusion theorems may be interpreted as a priori norm inequalities, too.

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Zusammenfassung Wir stellen Eigenwerteinschlußsätze vor, welche die Berechnung beiderseitiger Eigenwertschranken in Abhängigkeit von vorgelegten Näherungseigenpaaren gestatten. Wir demonstrieren an numerischen Beispielen, daß es mit dem Kollokationsverfahren möglich ist, sehr gute Einschlüsse selbst höherer Eigenwerte zu erhalten. Als Ansatzfunktionen bewähren sich Singularitätenfunktionen, welche eine Steuerbarkeit der numerischen Stabilität ermöglichen. Zudem erlauben diese Funktionen in der Theorie einen Einschluß in beliebiger Güte.Die Einschlußsätze können auch als a priori Norm-Ungleichungen angesehen werden.

     

The inclusion of Stekloff eigenvalues for nonsmooth bounded domains

The method used in [3] for including Stekloff eigenvalues is applied to domains with nonsmooth boundary. Considering special trial functions whose construction is adapted to the local singular behaviour of the eigenfunctions near corners leads to sharp eigenvalue intervals for rhombi and the L-shaped polygonal domain.

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Zusammenfassung Die in [3] zum Einschluß von Stekloff-Eigenwerten angewandte Methode wird erfolgreich für Gebiete mit nicht-glatten Rändern erprobt. Unter Verwendung von speziellen Ansatzfunktionen, deren Konstruktion das lokal singuläre Verhalten der Eigenlösungen in der Umgebung der Ecken berücksichtigt, werden bei Rhomben und dem L-förmigen Polygon enge Einschlüsse erreicht.

     

Persistence of embedded eigenvalues

We consider conditions under which an embedded eigenvalue of a self-adjoint operator remains embedded under small perturbations. In the case of a simple eigenvalue embedded in continuous spectrum of multiplicity m<∞ we show that in favorable situations, the set of small perturbations of a suitable Banach space which do not remove the eigenvalue form a smooth submanifold of codimension m. We also have results regarding the cases when the eigenvalue is degenerate or when the multiplicity of the continuous spectrum is infinite.     

On the distribution of Laplacian eigenvalues of trees

For a tree T$T$ with n$n$ vertices, we apply an algorithm due to Jacobs and Trevisan (2011) to study how the number of small Laplacian eigenvalues behaves when the tree is transformed by a transformation defined by Mohar (2007). This allows us to obtain a new bound for the number of eigenvalues that are smaller than 2. We also report our progress towards a conjecture on the number of eigenvalues that are smaller than the average degree.     

Sums of free membrane eigenvalues

LetD be a simply connected domain in the plane which is the image of the unit disk under a normalized conformal mapping, and let μ₁=0<μ₂≤μ₃ be the free membrane eigenvalues. We prove that for anyn≥2,

Condition of extremum for eigenvalues of elliptic boundary-value problems

In this paper, we consider problems of eigenvalue optimization for elliptic boundary-value problems. The coefficients of the higher derivatives are determined by the internal characteristics of the medium and play the role of control. The necessary conditions of the first and second order for problems of the first eigenvalue maximization are presented. In the case where the maximum is reached on a simple eigenvalue, the second-order condition is formulated as completeness condition for a system of functions in Banach space. If the maximum is reached on a double eigenvalue, the necessary condition is presented in the form of linear dependence for a system of functions. In both cases, the system is comprised of the eigenfunctions of the initial-boundary value problem. As an example, we consider the problem of maximization of the first eigenvalue of a buckling column that lies on an elastic foundation.     

Systematic occurrence of repeated eigenvalues in structural optimization

Examples of finite-dimensional structural design problems with constraints on natural frequency and buckling are used to demonstrate that repeated eigenvalues may be expected to occur when a structure is optimized. It is shown that a repeated eigenvalue is not generally differentiable with respect to design variables. Directional derivatives are shown to exist, and a method of calculating directional derivatives is given. Necessary conditions of optimality are derived and applied to a vibration optimization problem. Extensions of the theory to distributed-parameter structures and numerical methods are outlined.This research was supported by NSF Grant No. CMS-80-05677     

Laplacian eigenvalues and the maximum cut problem

We introduce and study an eigenvalue upper bound(G) on the maximum cut mc (G) of a weighted graph. The function(G) has several interesting properties that resemble the behaviour of mc (G). The following results are presented.We show that is subadditive with respect to amalgam, and additive with respect to disjoint sum and 1-sum. We prove that(G) is never worse that 1.131 mc(G) for a planar, or more generally, a weakly bipartite graph with nonnegative edge weights. We give a dual characterization of(G), and show that(G) is computable in polynomial time with an arbitrary precision.The research has been partially done when the second author visited LRI in September 1989.     

Simultaneous estimation of eigenvalues

The problem of simultaneous estimation of eigenvalues of covariance matrix is considered for one and two sample problems under a sum of squared error loss. New classes of estimators are obtained which dominate the best multiple of the sample eigenvalues in terms of risk. These estimators shrink or expand the sample eigenvalues towards their geometric mean. Similar results are obtained for the estimation of eigenvalues of the precision matrix and the residual matrix when the original covariance matrix is partitioned into two groups. As a consequence, a new estimator of trace of the covariance matrix is obtained.The results are extended to two sample problem where two Wishart distributions are independently observed, say, S _i W _p ( _i , k _i ), i=1, 2, and eigenvalues of _{1 2} ^-1 are estimated simultaneously. Finally, some numerical calculations are done to obtain the amount of risk improvement.     

On eigenvalues of spherical fractal drums

We will give better estimates of a kind of nonisotropic fractal drum.     

A Harnack inequality for Dirichlet eigenvalues

We prove a Harnack inequality for Dirichlet eigenfunctions of abelian homogeneous graphs and their convex subgraphs. We derive lower bounds for Dirichlet eigenvalues using the Harnack inequality. We also consider a randomization problem in connection with combinatorial games using Dirichlet eigenvalues. © 2000 John Wiley & Sons, Inc. J Graph Theory 34: 247–257, 2000     

On computing eigenvalues of second-order linear pencils

^** Email: mhannaby{at}yahoo.com^*** Email: zahraa26{at}yahoo.com In this paper, we use sinc techniques to compute the eigenvaluesof a second-order operator pencil of the form Q – P approximately.Here Q and P are self-adjoint differential operators of thesecond and first order, respectively. Also the eigenparameterappears in the boundary conditions linearly.     

On the eigenvalues of second-order boundary-value problems

In this paper we investigate the properties of eigenvalues of some boundary-value problems generated by second-order Sturm-Liouville equation with distributional potentials and suitable boundary conditions. Moreover, we share a necessary condition for the problem to have an infinitely many eigenvalues. Finally, we introduce some ordinary and Frechet derivatives of the eigenvalues with respect to some elements of the data.     

Iterative computation of derivatives of repeated eigenvalues and the corresponding eigenvectors

Recently the authors proposed a simultaneous iteration algorithm for the computation of the partial derivatives of repeated eigenvalues and the corresponding eigenvectors of matrices depending on several real variables. This paper analyses the properties of that algorithm and extends it in several ways. The previous requirement that the repeated eigenvalue be dominant is relaxed, and the new generalized algorithm given here allows the simultaneous treatment of simple and repeated eigenvalues. Methods for accelerating convergence are examined. Numerical results support our theoretical analysis. Copyright © 2000 John Wiley & Sons, Ltd.     

Lower and upper bounds of Dirichlet eigenvalues for totally characteristic degenerate elliptic operators

Let λkbe the k-th Dirichlet eigenvalue of totally characteristic degenerate elliptic operator-ΔB defined on a stretched cone B0 ■ [0,1) × X with boundary on {x1 = 0}. More precisely,ΔB=(x1αx1)2+ α2x2+ + α2xnis also called the cone Laplacian. In this paper,by using Mellin-Fourier transform,we prove thatλk Cnk2 n for any k 1,where Cn=(nn+2)(2π)2(|B0|Bn)-2n,which gives the lower bounds of the Dirchlet eigenvalues of-ΔB. On the other hand,by using the Rayleigh-Ritz inequality,we deduce the upper bounds ofλk,i.e.,λk+1 1 +4n k2/nλ1. Combining the lower and upper bounds of λk,we can easily obtain the lower bound for the first Dirichlet eigenvalue λ1 Cn(1 +4n)-12n2.     

L-invariants and logarithm derivatives of eigenvalues of Frobenius

Let K be a p-adic local field.We study a special kind of p-adic Galois representations of it.These representations are similar to the Galois representations occurred in the exceptional zero conjecture for modular forms.In particular,we verify that a formula of Colmez can be generalized to our case.We also include a degenerated version of Colmez’s formula.